The present invention relates generally to silicone compositions, and in particular, to emulsions comprising a branched trimethylsilylated alkylsilsesquioxane.
Aqueous emulsions of polydimethylsiloxane fluids have been applied to many surfaces as a protective coating. Such surfaces include for example, rubber, vinyl, plastic, and leather. Some of these surfaces are said to have been rendered anti-static for the purpose of repelling dust and dirt. When these emulsions are employed as protective coatings in outdoor applications, such as the sidewall of an automotive tire, the polydimethylsiloxane coating is rapidly removed by water which is encountered when the tire is exposed to rain or snow. In order to restore the protective coating to the tire, another application of the polydimethylsiloxane emulsion is required. This is time consuming and a repeated expense, and thus, reduces consumer acceptance. Exemplary of such polydimethylsiloxane emulsion coatings are U.S. Pat. No. 3,956,174, issued May 11, 1976 and U.S. Pat. No. 4,133,921, issued Jan. 9, 1979.
Recognizing the deficiencies of polydimethylsiloxane fluids, aqueous emulsions of linear polymethylalkylsiloxanes are disclosed in U.S. Pat. No. 5,017,221, issued May 21, 1991. U.S. Pat. No. 5,017,221 states that coatings on organic substrates produced from these emulsions, when exposed to rain and snow in outdoor applications, were less readily removed from the substrate than polydimethylsiloxane coatings. The alleged increased efficacy of the coatings derived from the linear polymethylalkylsiloxane emulsions was believed to be due to the presence of the alkyl groups which have a strong affinity for organic surfaces including rubber and plastics. Coatings derived from polymethylalkylsiloxanes, however, are also believed to be susceptible to degradation or removal from the substrate upon exposure to inclement weather. The inability of these polymethylalkylsiloxane coatings to resist inclement weather is likely attributable to the fact that such compounds are generally linear, and in consequence, such coatings tend to lay on the surface of the substrate to which they are applied, rather than be absorbed by the interstices within the substrate. Additionally, polymethylalkylsiloxanes coatings, as stated in U.S. Pat. No. 5,017,221, produce a glossy, lusterous appearance, which in turn deleteriously affects consumer acceptance when the coating is to be applied to certain substrates, such as, for example, automobile tires.
A need therefore exists for a compound capable of forming an aqueous emulsion to be used in protective coatings which exhibits prolonged adherence to a substrate, and produces a non-glossy or matte appearance.
The present invention is directed to an emulsion, and a protective coating, which includes a branched trimethylsilylated alkylsilsesquioxane with the formula:
Me3SiO[R(Me3SiO)SiO]xSiMe3
wherein R is a substituted or unsubstituted linear or branched monovalent hydrocarbon substituent with from 6 to 14 carbon atoms, Me is Methyl, and x ranges from 1 to 6.
According to another aspect of the invention, a method of rendering an organic surface repellent to fluids and particulates includes treating the substrate with an emulsion having a branched trimethylsilylated alkylsilsesquioxane.
The protective coating formed with the trimethylsilylated alkylsilsesquioxane exhibits superior resistance to degradation caused by inclement weather and thus minimizes the need for repeated applications, while providing a matte appearance which is aesthetically appealing to consumers.
These and other objects, advantages, purposes and features of the invention will become apparent upon review of the following detailed description.
The present invention relates to a protective coating for treating organic substrates which renders the same repellant to fluids and particulate matter, such as, for example, water, snow, road salt, dirt, debris, etc., The protective coating includes a branched, non-linear, trimethylsilylated alkylsilsesquioxane. In a preferred form, the protective coating is in the form of an emulsion.
The protective coating of the present invention may be used to treat a wide variety of organic substrates. Non-limiting examples of organic substrates include rubber substrates such as wires, cables, the sidewall of automotive tires, footwear, and coated fabrics; and synthetic plastic substrates such as automotive dashboards, automotive trim (both interior and exterior), automotive upholstery, flooring, residential siding, and piping.
The branched trimethylsilylated alkylsilsesquioxane has the following branched, non-linear structure: 
wherein R is a substituted or unsubstituted linear or branched monovalent hydrocarbon substituent with from 6 to 14 carbon atoms, Me is Methyl, and x ranges from 1 to 6. For example, R, having from 6 to 14 carbon atoms, may be hexyl, n-hexyl, 2-(perfluorobutyl)ethyl, heptyl, octyl, n-octyl, 1-(perfluorohexyl)ethyl, nonyl, decyl, dodecyl, tetradecyl and the like, or may comprise any other monovalent hydrocarbon substituent known to those of ordinary skill in the art. Additionally, it is contemplated herein that each R may be the same or different monovalent hydrocarbon substituent. The value of x in the above formula for the trimethylsilylated alklysilsesquioxane for the most preferred embodiment ranges from 2 to about 6.
Preferably, the branched trimethylsilylated alkylsilsesquioxane is a fluid and has a high purity which is substantially free of polydimethylsiloxanes, organic and inorganic chemicals. The synthesis of the high purity branched trimethylsilylated alkylsilsesquioxane fluid is disclosed in U.S. Pat. No. 5,932,231, issued Aug. 3, 1999, the entire disclosure of which is hereby incorporated herein by reference. The high purity branched trimethylsilylated alkylsilsesquioxane fluid has a viscosity in the range from about 20 centistoke to about 1000 centistoke, measured at 25 degrees Centigrade, preferably 200 to 500 centistoke, with a viscosity between 300 and 400 centistoke being the most preferred. As stated hereinabove, the protective coating is preferably in the form of an emulsion comprising the branched trimethylsilylated alkylsilsesquioxane fluid, a continuous phase, or carrier liquid, and a surfactant. The carrier liquid may be mineral oil, vegetable oil, polydimethyl silicones, cyclic siloxanes, water, methylsiloxanes having a viscosity of less than about ten centistokes including, but not limited to cyclopolysiloxanes of the formula [(CH3)2SiO]x and linear siloxanes of the formula (CH3)3SiO[(CH3)2Si]ySi(CH3)3 in which x is an integer having a value of from three to ten and y is an integer having a value of from zero to about four; hydrocarbons having from about six to sixteen carbon atoms including straight and branched chains. Preferably, the carrier liquid is water. The surfactant can be cationic, anionic, non-ionic, silicone-modified, silicone copolyols or mixtures thereof. The concentration of carrier liquid should be sufficient to enable the emulsion to be readily dispensed from a typical household container with or without the aid of an adjustable spray head. In a preferred form, the emulsion also includes a polyglycol, non-limiting examples of which include ethylene glycol, propylene glycol, butylene glycol, mixtures thereof, and copolymers thereof. The polyglycol reduces the surface tension of the water with respect to the substrate and thereby improves the spreading of the continuous phase of the emulsion.
The branched trimethylsilylated alkylsilsesquioxane is present in an amount between approximately 5% and 35% by weight, preferably between approximately 15% and 25%. The carrier liquid used is between approximately 65% and 95%, preferably 75% and 85%; while the surfactant concentration is between approximately 1% and 5%; preferably between approximately 2% and 3%. If a polyglycol is employed, it is present in an amount between approximately 0.1% and 1.0%, preferably between 0.2% and 0.6%. The emulsion can be made in accordance with any emulsion technique commonly employed by those with ordinary skill in the art.
While not wishing to be bound by theory, the enhanced functional benefits of the protective coatings of the present invention are believed to be attributable to the greater ability of the branched trimethylsilylated alkylsilsesquioxane fluids to spread on the organic surface of the substrate and to penetrate said surface. That is, the branched, three dimensional structure of the trimethylsilylated alkylsilsesquioxane fluids is believed to enable the compound to be absorbed by the interstitial spaces present in the organic substrate to which it is applied. The trimethylsiloxy group content of the branched trimethylsilylated alkylsilsesquioxane fluids is far greater than that present in either polydimethylsiloxane or linear polyalkylmethylsiloxane fluids of similar viscosity. Table I shows the calculated % trimethylsiloxy content of the three types of polymers.
In addition, the molecular weight of the branched trimethylsilylated alkylsilsesquioxanes of 350 cs viscosity is significantly lower than the molecular weights of polydimethylsiloxane or linear polyalkylmethylsiloxanes of the same viscosity. Thus, the smaller, largely spherical molecules of the branched trimethylsilylated alkylsilsesquioxanes are able to spread on organic substrates and penetrate the substrate""s pores better than the other types of silicones and then, because of their high alkyl content, are held there more tenaciously. Another significant difference between the protective coatings formed of trimethylsilylated octylsilsesquioxane and commercially available tire treatments containing polydimethylsiloxanes is the fact that the coatings according to the present invention are not shiny; rather, they have a matte appearance within a few hours of being applied. This matte appearance does not change with time.